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78 lines
3.2 KiB
C++
78 lines
3.2 KiB
C++
#pragma once
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#include <DB/Columns/IColumn.h>
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#include <DB/Columns/ColumnsNumber.h>
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namespace DB
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{
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using NullValuesByteMap = PaddedPODArray<UInt8>;
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/// Class that specifies nullable columns. A nullable column represents
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/// a column, which may have any type, provided with the possibility of
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/// storing NULL values. For this purpose, a ColumNullable object stores
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/// an ordinary column along with a special column, namely a byte map,
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/// whose type is ColumnUInt8. The latter column indicates whether the
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/// value of a given row is a NULL or not. Such a design is preferred
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/// over a bitmap because columns are usually stored on disk as compressed
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/// files. In this regard, using a bitmap instead of a byte map would
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/// greatly complicate the implementation with little to no benefits.
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class ColumnNullable final : public IColumn
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{
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public:
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ColumnNullable(ColumnPtr nested_column_);
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ColumnNullable(ColumnPtr nested_column_, bool fill_with_nulls);
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std::string getName() const override;
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bool isNullable() const override;
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ColumnPtr cloneResized(size_t size) const override;
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size_t size() const override;
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bool isNullAt(size_t n) const;
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Field operator[](size_t n) const override;
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void get(size_t n, Field & res) const override;
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UInt64 get64(size_t n) const override;
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StringRef getDataAt(size_t n) const override;
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void insertData(const char * pos, size_t length) override;
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StringRef serializeValueIntoArena(size_t n, Arena & arena, char const *& begin) const override;
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const char * deserializeAndInsertFromArena(const char * pos) override;
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void insertRangeFrom(const IColumn & src, size_t start, size_t length) override;;
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void insert(const Field & x) override;
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void insertDefault() override;
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void popBack(size_t n) override;
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ColumnPtr filter(const Filter & filt, ssize_t result_size_hint) const override;
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ColumnPtr permute(const Permutation & perm, size_t limit) const override;
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int compareAt(size_t n, size_t m, const IColumn & rhs_, int null_direction_hint) const override;
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void getPermutation(bool reverse, size_t limit, Permutation & res) const override;
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void reserve(size_t n) override;
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size_t byteSize() const override;
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ColumnPtr replicate(const Offsets_t & replicate_offsets) const override;
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ColumnPtr convertToFullColumnIfConst() const override;
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void updateHashWithValue(size_t n, SipHash & hash) const override;
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void getExtremes(Field & min, Field & max) const override;
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/// Return the column that represents values.
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ColumnPtr & getNestedColumn();
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const ColumnPtr & getNestedColumn() const;
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/// Return the column that represents the byte map.
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ColumnPtr & getNullValuesByteMap();
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const ColumnPtr & getNullValuesByteMap() const;
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/// Apply the null byte map of a specified nullable column onto the
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/// null byte map of the current column by performing an element-wise OR
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/// between both byte maps. This method is used to determine the null byte
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/// map of the result column of a function taking one or more nullable
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/// columns.
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void applyNullValuesByteMap(const ColumnNullable & other);
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private:
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/// Convenience methods which make the implementation easier to read.
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ColumnUInt8 & getNullMapContent();
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const ColumnUInt8 & getNullMapContent() const;
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private:
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ColumnPtr nested_column;
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ColumnPtr null_map;
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};
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}
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